Manual and information tutorial about systemd.service

SYSTEMD.SERVICE(5)systemd.serviceSYSTEMD.SERVICE(5)NAMEsystemd.service - systemd service configuration files
SYNOPSISsystemd.serviceDESCRIPTION
A unit configuration file whose name ends in .service encodes
information about a process controlled and supervised by systemd.
This man page lists the configuration options specific to this unit
type. See systemd.unit(5) for the common options of all unit
configuration files. The common configuration items are configured in
the generic [Unit] and [Install] sections. The service specific
configuration options are configured in the [Service] section.
Additional options are listed in systemd.exec(5), which define the
execution environment the commands are executed in.
Unless DefaultDependencies= is set to false, service units will
implicitly have dependencies of type Requires= and After= on
basic.target as well as dependencies of type Conflicts= and Before= on
shutdown.target. These ensure that normal service units pull in basic
system initialization, and are terminated cleanly prior to system
shutdown. Only services involved with early boot or late system
shutdown should disable this option.
If a service is requested under a certain name but no unit
configuration file is found, systemd looks for a SysV init script by
the same name (with the .service suffix removed) and dynamically
creates a service unit from that script. This is useful for
compatibility with SysV.
OPTIONS
Service files must include a [Service] section, which carries
information about the service and the process it supervises. A number
of options that may be used in this section are shared with other unit
types. These options are documented in systemd.exec(5). The options
specific to the [Service] section of service units are the following:
Type=
Configures the process start-up type for this service unit. One of
simple, forking, oneshot, dbus, notify.
If set to simple (the default value) it is expected that the
process configured with ExecStart= is the main process of the
service. In this mode, if the process offers functionality to other
processes on the system its communication channels should be
installed before the daemon is started up (e.g. sockets set up by
systemd, via socket activation), as systemd will immediately
proceed starting follow-up units.
If set to forking it is expected that the process configured with
ExecStart= will call fork() as part of its start-up. The parent
process is expected to exit when start-up is complete and all
communication channels set up. The child continues to run as the
main daemon process. This is the behaviour of traditional UNIX
daemons. If this setting is used, it is recommended to also use the
PIDFile= option, so that systemd can identify the main process of
the daemon. systemd will proceed starting follow-up units as soon
as the parent process exits.
Behaviour of oneshot is similar to simple, however it is expected
that the process has to exit before systemd starts follow-up units.
RemainAfterExit= is particularly useful for this type of service.
Behaviour of dbus is similar to simple, however it is expected that
the daemon acquires a name on the D-Bus bus, as configured by
BusName=. systemd will proceed starting follow-up units after the
D-Bus bus name has been acquired. Service units with this option
configured implicitly gain dependencies on the dbus.target unit.
Behaviour of notify is similar to simple, however it is expected
that the daemon sends a notification message via sd_notify(3) or an
equivalent call when it finished starting up. systemd will proceed
starting follow-up units after this notification message has been
sent. If this option is used NotifyAccess= (see below) should be
set to open access to the notification socket provided by systemd.
If NotifyAccess= is not set, it will implicitly be set to main.
RemainAfterExit=
Takes a boolean value that specifies whether the service shall be
considered active even when all its processes exited. Defaults to
no.
PIDFile=
Takes an absolute file name pointing to the PID file of this
daemon. Use of this option is recommended for services where Type=
is set to forking.
BusName=
Takes a D-Bus bus name, where this service is reachable as. This
option is mandatory for services where Type= is set to dbus, but
its use is otherwise recommended as well if the process takes a
name on the D-Bus bus.
ExecStart=
Takes a command line that is executed when this service shall be
started up. The first token of the command line must be an absolute
file name, then followed by arguments for the process. It is
mandatory to set this option for all services. This option may not
be specified more than once, except when Type=oneshot is used in
which case more than one ExecStart= line is accepted which are then
invoked one by one, sequentially in the order they appear in the
unit file.
Optionally, if the absolute file name is prefixed with @, the
second token will be passed as argv[0] to the executed process,
followed by the further arguments specified. If the first token is
prefixed with - an exit code of the command normally considered a
failure (i.e. non-zero exit status or abnormal exit due to signal)
is ignored and considered success. If both - and @ are used for the
same command the former must precede the latter. Unless
Type=forking is set, the process started via this command line will
be considered the main process of the daemon. The command line
accepts % specifiers as described in systemd.unit(5). On top of
that basic environment variable substitution is supported, where
${FOO} is replaced by the string value of the environment variable
of the same name. Also $FOO may appear as separate word on the
command line in which case the variable is replaced by its value
split at whitespaces. Note that the first argument (i.e. the binary
to execute) may not be a variable, and must be a literal and
absolute path name.
ExecStartPre=, ExecStartPost=
Additional commands that are executed before (resp. after) the
command in ExecStart=. Multiple command lines may be concatenated
in a single directive, by separating them by semicolons (these
semicolons must be passed as separate words). In that case, the
commands are executed one after the other, serially. Alternatively,
these directives may be specified more than once with the same
effect. However, the latter syntax is not recommended for
compatibility with parsers suitable for XDG .desktop files. Use of
these settings is optional. Specifier and environment variable
substitution is supported.
ExecReload=
Commands to execute to trigger a configuration reload in the
service. This argument takes multiple command lines, following the
same scheme as pointed out for ExecStartPre= above. Use of this
setting is optional. Specifier and environment variable
substitution is supported here following the same scheme as for
ExecStart=. One special environment variable is set: if known
$MAINPID is set to the main process of the daemon, and may be used
for command lines like the following: /bin/kill -HUP $MAINPID.
ExecStop=
Commands to execute to stop the service started via ExecStart=.
This argument takes multiple command lines, following the same
scheme as pointed out for ExecStartPre= above. Use of this setting
is optional. All processes remaining for a service after the
commands configured in this option are run are terminated according
to the KillMode= setting (see below). If this option is not
specified the process is terminated right-away when service stop is
requested. Specifier and environment variable substitution is
supported (including $MAINPID, see above).
ExecStopPost=
Additional commands that are executed after the service was stopped
using the commands configured in ExecStop=. This argument takes
multiple command lines, following the same scheme as pointed out
for ExecStartPre. Use of these settings is optional. Specifier and
environment variable substitution is supported.
RestartSec=
Configures the time to sleep before restarting a service (as
configured with Restart=). Takes a unit-less value in seconds, or a
time span value such as "5min 20s". Defaults to 100ms.
TimeoutSec=
Configures the time to wait for start-up and stop. If a daemon
service does not signal start-up completion within the configured
time the service will be considered failed and be shut down again.
If a service is asked to stop but does not terminate in the
specified time it will be terminated forcibly via SIGTERM, and
after another delay of this time with SIGKILL. (See KillMode=
below.) Takes a unit-less value in seconds, or a time span value
such as "5min 20s". Pass 0 to disable the timeout logic. Defaults
to 60s.
Restart=
Configures whether the main service process shall be restarted when
it exits. Takes one of no, on-success, on-failure, on-abort or
always. If set to no (the default) the service will not be
restarted when it exits. If set to on-success it will be restarted
only when it exited cleanly, i.e. terminated with an exit code of
0. If set to on-failure it will be restarted only when it exited
with an exit code not equalling 0, or when terminated by a signal.
If set to on-abort it will be restarted only if it exits due to
reception of an uncaught signal. If set to always the service will
be restarted regardless whether it exited cleanly or not, or got
terminated abnormally by a signal.
PermissionsStartOnly=
Takes a boolean argument. If true, the permission related execution
options as configured with User= and similar options (see
systemd.exec(5) for more information) are only applied to the
process started with ExecStart=, and not to the various other
ExecStartPre=, ExecStartPost=, ExecReload=, ExecStop=,
ExecStopPost= commands. If false, the setting is applied to all
configured commands the same way. Defaults to false.
RootDirectoryStartOnly=
Takes a boolean argument. If true, the root directory as configured
with the RootDirectory= option (see systemd.exec(5) for more
information) is only applied to the process started with
ExecStart=, and not to the various other ExecStartPre=,
ExecStartPost=, ExecReload=, ExecStop=, ExecStopPost= commands. If
false, the setting is applied to all configured commands the same
way. Defaults to false.
SysVStartPriority=
Set the SysV start priority to use to order this service in
relation to SysV services lacking LSB headers. This option is only
necessary to fix ordering in relation to legacy SysV services, that
have no ordering information encoded in the script headers. As such
it should only be used as temporary compatibility option, and not
be used in new unit files. Almost always it is a better choice to
add explicit ordering directives via After= or Before=, instead.
For more details see systemd.unit(5). If used, pass an integer
value in the range 0-99.
KillMode=
Specifies how processes of this service shall be killed. One of
control-group, process-group, process, none.
If set to control-group all remaining processes in the control
group of this service will be terminated on service stop, after the
stop command (as configured with ExecStop=) is executed. If set to
process-group only the members of the process group of the main
service process are killed. If set to process only the main process
itself is killed. If set to none no process is killed. In this case
only the stop command will be executed on service stop, but no
process be killed otherwise. Processes remaining alive after stop
are left in their control group and the control group continues to
exist after stop unless it is empty. Defaults to control-group.
Processes will first be terminated via SIGTERM (unless the signal
to send is changed via KillSignal=). If then after a delay
(configured via the TimeoutSec= option) processes still remain, the
termination request is repeated with the SIGKILL signal (unless
this is disabled via the SendSIGKILL= option). See kill(2) for more
information.
KillSignal=
Specifies which signal to use when killing a service. Defaults to
SIGTERM.
SendSIGKILL=
Specifies whether to send SIGKILL to remaining processes after a
timeout, if the normal shutdown procedure left processes of the
service around. Takes a boolean value. Defaults to "yes".
NonBlocking=
Set O_NONBLOCK flag for all file descriptors passed via
socket-based activation. If true, all file descriptors >= 3 (i.e.
all except STDIN/STDOUT/STDERR) will have the O_NONBLOCK flag set
and hence are in non-blocking mode. This option is only useful in
conjunction with a socket unit, as described in systemd.socket(5).
Defaults to false.
NotifyAccess=
Controls access to the service status notification socket, as
accessible via the sd_notify(3) call. Takes one of none (the
default), main or all. If none no daemon status updates are
accepted from the service processes, all status update messages are
ignored. If main only service updates sent from the main process of
the service are accepted. If all all services updates from all
members of the service's control group are accepted. This option
must be set to open access to the notification socket when using
Type=notify (see above).
Sockets=
Specifies the name of the socket units this service shall inherit
the sockets from when the service (ignoring the different suffix of
course) is started. Normally it should not be necessary to use this
setting as all sockets whose unit shares the same name as the
service are passed to the spawned process.
Note that the same socket may be passed to multiple processes at
the same time. Also note that a different service may be activated
on incoming traffic than inherits the sockets. Or in other words:
The Service= setting of .socket units doesn't have to match the
inverse of the Sockets= setting of the .service it refers to.
FsckPassNo=
Set the fsck passno priority to use to order this service in
relation to other file system checking services. This option is
only necessary to fix ordering in relation to fsck jobs
automatically created for all /etc/fstab entries with a value in
the fs_passno column > 0. As such it should only be used as option
for fsck services. Almost always it is a better choice to add
explicit ordering directives via After= or Before=, instead. For
more details see systemd.unit(5). If used, pass an integer value in
the same range as /etc/fstab's fs_passno column. See fstab(5) for
details.
SEE ALSOsystemd(1), systemctl(8), systemd.unit(5), systemd.exec(5)AUTHOR
Lennart Poettering <lennart@poettering.net>
Developer
systemd 01/22/2011 SYSTEMD.SERVICE(5)